[GHC] #9600: Bad error message: Applicative is not a derivable class

[GHC]

#9600: Bad error message: Applicative is not a derivable class
-------------------------------------+-------------------------------------
        Reporter:  nh2               |                   Owner:
                                     |  JohnWiegley
            Type:  bug               |                  Status:  new
        Priority:  normal            |               Milestone:  7.12.1
       Component:  Compiler          |                 Version:  7.8.3
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:                    |  Differential Revisions:  Phab:D216
-------------------------------------+-------------------------------------

Comment (by Ben Gamari <ben@…>):

 In [changeset:"4f80ec0ee438800d95673a4898e69371957fed09/ghc"
 4f80ec0e/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="4f80ec0ee438800d95673a4898e69371957fed09"
 Improve error message for newtypes and deriving clauses

 Summary:
 Change the error message generated when a deriving clause related to a
 newtype
 fails to always suggested trying GeneralizedNewtypeDeriving, even in
 situations where it may not work. Fixes #9600.

 Test Plan: testsuite/deriving/should_fail/9600.hs

 Reviewers: austin, bgamari, simonpj

 Rebased-by: bgamari

 Reviewed By: simonpj

 Subscribers: bgamari, hvr, simonmar, carter

 Differential Revision: https://phabricator.haskell.org/D216

 GHC Trac Issues: #9600
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9600#comment:5>
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